Method and apparatus for transmitting and receiving legacy format data in high throughput wireless network

ABSTRACT

A method and an apparatus are provided for enabling a legacy station to perform virtual carrier sensing when a plurality of stations with heterogeneous capabilities coexist in a wireless network. The method includes receiving first data compliant with a first protocol, and transmitting second data compliant with a second protocol, where the first protocol is downward compatible with the second protocol.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application No.10-2005-0049444 filed on Jun. 9, 2005 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Methods and apparatuses consistent with the present invention relate totransmitting and receiving legacy format data in a high throughputwireless network.

2. Description of the Related Art

Recently, there has been an increasing demand for ultra high-speedcommunication networks due to widespread public use of the Internet anda rapid increase in the amount of available multimedia data. Since localarea networks (LANs) emerged in the late 1980s, the data transmissionrate over the Internet has drastically increased from about 1 Mbps toabout 100 Mbps. Thus, high-speed Ethernet transmission has gainedpopularity and wide spread use. Currently, intensive research into agigabit-speed Ethernet is under way. An increasing interest in thewireless network connection and communication has triggered researchinto and development of wireless LANs (WLANs), and greatly increasedavailability of WLANs to consumers. Although use of WLANs may reduceperformance due to lower transmission rate and poorer stability ascompared to wired LANs, WLANs have various advantages, includingwireless networking capability, greater mobility and so on. Accordingly,WLAN markets have been gradually growing.

Due to the need for a higher transmission rate and the development ofwireless transmission technology, the initial Institute of Electricaland Electronics Engineers (IEEE) 802.11 standard, which specifies atransfer rate of 1 to 2 Mbps, has evolved into advanced standardsincluding IEEE 802.11 a, 802.11b and 802.11g. The IEEE 802.11g standard,which utilizes a transmission rate of 6 to 54 Mbps in the 5 GHz-NationalInformation Infrastructure (NII) band, uses orthogonal frequencydivision multiplexing (OFDM) as its transmission technology. With anincreasing public interest in OFDM transmission and use of a 5 GHz-band,much greater attention is been paid to the IEEE 802.11g standard andOFDM transmission technology than to other wireless standards.

Recently, wireless Internet services using WLAN, so-called “Nespot,”have been launched and offered by Korea Telecommunication (KT)Corporation of Korea. Nespot services allow access to the Internet usinga WLAN according to IEEE 802.11 b standard, commonly called Wi-Fi(wireless fidelity). Communication standards for wireless datacommunication systems, which have been completed and promulgated or arebeing researched and discussed, include Wide Code Division MultipleAccess (WCDMA), IEEE 802.11x, Bluetooth, IEEE 802.15.3, etc., which areknown as 3rd Generation (3G) communication standards. The most widelyknown, cheapest wireless data communication standard is IEEE 802.11b, aseries of IEEE 802.11x. An IEEE 802.11b WLAN standard delivers datatransmission at a maximum rate of 11 Mbps and utilizes the 2.4GHz-Industrial, Scientific, and Medical (ISM) band, which can be usedbelow a predetermined electric field without permission. With the recentwidespread use of the IEEE 802.11a WLAN standard, which delivers amaximum data rate of 54 Mbps in the 5 GHz-band by using OFDM, IEEE802.11g developed as an extension to the IEEE 802.11a standard for datatransmission in the 2.4 GHz-band using OFDM and is intensively beingresearched.

The Ethernet and the WLAN, which are currently being widely used, bothutilize a carrier sensing multiple access (CSMA) method. According tothe CSMA method, it is determined whether a channel is in use. If thechannel is not in use, that is, if the channel is idle, then data istransmitted. If the channel is busy, retransmission of data is attemptedafter a predetermined period of time has elapsed. A carrier sensingmultiple access with collision detection (CSMA/CD) method, which is animprovement of the CSMA method, is used in a wired LAN, whereas acarrier sensing multiple access with collision avoidance (CSMA/CA)method is used in packet-based wireless data communications. In theCSMA/CD method, a station suspends transmitting signals if a collisionis detected during transmission. Compared with the CSMA method, whichpre-checks whether a channel is occupied before transmitting data, inthe CSMA/CD method, the station suspends transmission of signals when acollision is detected during the transmission of signals and transmits ajam signal to another station to inform it of the occurrence of thecollision. After the transmission of the jam signal, the station has arandom backoff period for delay and restarts transmitting signals. Inthe CSMA/CD method, the station does not transmit data immediately evenafter the channel becomes idle and has a random backoff period for apredetermined duration before transmission to avoid collision ofsignals. If a collision of signals occurs during transmission, theduration of the random backoff period is increased by two times, therebyfurther lowering a probability of collision.

The CSMA/CA method is classified into physical carrier sensing andvirtual carrier sensing. Physical carrier sensing refers to the physicalsensing of active signals in the wireless medium. Virtual carriersensing is performed such that information regarding duration of amedium occupation is set to a media access control (MAC) protocol dataunit / physical (PHY) service data unit (MPDU/PSDU) and transmission ofdata is then started after the estimated duration has elapsed. However,if the MPDU/PSDU cannot be interpreted, the virtual carrier sensingmechanism cannot be adopted.

IEEE 802.11n provides coverage for IEEE 802.11a networks at 5 GHz andIEEE 802.11g networks at 2.4 GHz and enables stations of various datarates to coexist. For operating the stations of various data rates usingthe CSMA/CA method, the stations must interpret MPDU/PSDU. However, somestations, that is, legacy stations, may not often process datatransmitted/received at high rates. In such a case, the legacy stationscannot perform virtual carrier sensing.

FIG. 1 is a data structure of a related art format Physical LayerConvergence Procedure (PLCP) Protocol Data Unit (PPDU) as defined by theIEEE 802.11a protocol. The PPDU includes a PLCP header and PhysicalLayer Service Data Unit (PSDU). A data rate field 3 and a data lengthfield 4 are used to determine a length of a data field that follows thePLCP header of the PPDU. The data rate field 3 and the data length field4 are also used to determine the time of the data being received ortransmitted, thereby performing virtual carrier sensing. In addition, ina case where a Message Protocol Data Unit (MPDU) is accurately filteredfrom the received PPDU, a “Dur/ID” field, which is one field among theheader fields of the MPDU, is interpreted and the medium is virtuallydetermined to be busy for an expected use time period of the medium. Ina case where a preamble field and a signal field of a PPDU frame beingreceived are only erroneously interpreted, media may attempt datatransmission by a backoff at a predetermined Extended Inter-Frame Space(EIFS), which is longer than a Distributed Coordination Function (DCF)Inter-Frame Space (DIFS), so that fairness in media access of allstations available in DCF is not ensured.

In a network where an existing station using a conventional protocol ora legacy station and a High Throughput (HT) station coexist, the legacystation may be upgraded for transmission and reception of HT data.However, a legacy station or a conventional station cannot performvirtual carrier sensing because these stations cannot interpret the“Dur/ID” field present in the data which was transmitted and received bythe HT station.

FIG. 2 is a diagram illustrating that a legacy station with a lowtransmission rate is incapable of performing virtual carrier sensingwhen a plurality of stations having a variety of transmissioncapabilities coexist.

A transmitter-side high throughput station (abbreviated astransmitter-side HT STA) 101 is a station complying with the IEEE802.11n protocols and operating using a channel bonding technique or amultiple input multiple output (MIMO) technique. Channel bonding is amechanism in which data frames are simultaneously transmitted over twoadjacent channels. In other words, according to a channel bondingtechnique, since two adjacent channels are bonded during datatransmission, channel extension exists. The MIMO technique is one typeof adaptive array antenna technology that electrically controlsdirectivity using a plurality of antennas. Specifically, in an MIMOsystem, directivity is enhanced using a plurality of antennas bynarrowing a beam width, thereby forming a plurality of transmissionpaths that are independent from one another. Accordingly, a datatransmission speed of a device that adopts the MIMO system increases asmany times as there are antennas in the MIMO system. In this regard,when data is transmitted/received using the channel bonding or MIMOtechnique, capable stations can read the transmitted/received data butincapable stations, i.e., legacy stations, cannot read thetransmitted/received data. Physical carrier sensing enables a physicallayer to inform an MAC layer whether a channel is busy or idle bydetecting whether the physical layer has received a predetermined levelof reception power. Thus, the physical carrier sensing is not associatedwith interpreting of data transmitted and received.

If the transmitter-side HT STA 101 transmits HT data, a receiver-side HTSTA 102 receives the HT data and transmits an HT acknowledgement (Ack)to the transmitter-side HT STA 101 in response to the received HT data.An additional HT STA 103 is able to interpret the HT data and the HTAck. Assuming a duration in which the HT data and the HT Ack aretransmitted and received, is set to a Network Allocation Vector (NAV),the medium is considered as being busy. Then, the additional HT STA 103waits for an DIFS after the lapse of an NAV period of time, and thenperforms a random backoff, and finally transmits data.

Meanwhile, a legacy station 201 is a station complying with the IEEE802.11a, 802.11b, or 802.11g protocols but is incapable of interpretingHT data. Thus, after a duration of the HT Ack is checked by physicalcarrier sensing, the legacy station 201 waits for the duration of anEIFS and then perform a backoff. Thus, the legacy station 201 waitslonger than other stations, that is, the transmitter-side HT STA 101,the receiver-side HT STA 102 and the additional HT STA 103, before beingassigned media, thereby adversely affecting data transmissionefficiency.

The IEEE 802.11 standard specifies a control response frame, such as anACK, a Request-to-Send (RTS) or a Clear-to-Send (CTS) frame, istransmitted at the same data rate as the directly previous frame.However, if the control response frame cannot be transmitted at the samedata rate as the directly previous frame, it must be transmitted at ahighest rate in a basic service set (BSS) as specified in the IEEE802.11 standard. In addition, unlike the legacy format data, the HT datahas HT preamble and HT signal fields added thereto, which leads to anincrease in the overhead of an PPDU, which may cause the ACK frame toresult in deteriorated performance compared to the legacy format PPDU.That is to say, the length of the legacy format PPDU complying with theIEEE 802.11a standard is approximately 20 λs while the length of a newlydefined HT PPDU is 40 λs or greater.

Consequently, there exists a need for enhancing performance of networkutilization by transmitting legacy format data, e.g., an ACK frame,without an HT preamble when a legacy station cannot interpret datatransmitted from an HT station, which may prevent virtual carriersensing from being performed properly.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for enabling alegacy station to perform virtual carrier sensing when a plurality ofstations with heterogeneous capabilities coexist in a wireless network.

The present invention also provides a method and apparatus fortransmitting and receiving legacy format data in a high throughputwireless network.

According to an aspect of the present invention, there is provided amethod of transmitting legacy format data in a high throughput (HT)wireless network, the method comprising accessing the wireless network,allowing the first station to receive first data compliant with a firstprotocol, and transmitting second data compliant with a second protocolto the first station, where the first protocol provides downwardcompatibility with the second protocol.

According to another aspect of the present invention, there is provideda method of receiving legacy format data, the method comprising allowinga first station to access to the wireless network, transmitting firstdata compliant with a first protocol to the first station, and receivingsecond data compliant with a second protocol, where the first protocolprovides downward compatibility with the second protocol.

According to still another aspect of the present invention, there isprovided an apparatus of transmitting and receiving legacy format datain a high throughput (HT) wireless network, the apparatus comprising atransmitting unit transmitting first data compliant with a firstprotocol to the wireless network or second data compliant with a secondprotocol, where the first protocol provides downward compatibility withthe second protocol, a receiving unit receiving data from the wirelessnetwork, and a legacy transmission controlling unit controlling thetransmitting unit to transmit the second data in accordance with thesecond protocol.

According to a further aspect of the present invention, there isprovided a method of transmitting data in a wireless network, the methodcomprising allowing a first station to access the wireless network,receiving first data using channel bonding, the first data transmittedfrom the first station, and transmitting an ACK frame to respectivechannels associated with the channel bonding.

According to yet another aspect of the present invention, there isprovided a wireless network apparatus comprising a receiving unitaccessing a wireless network and receiving first data transmitted from afirst station accessed to the wireless network using channel bonding,and a transmitting unit transmitting an ACK frame to channels associatedwith the channel bonding.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will become moreapparent by describing in detail exemplary embodiments thereof withreference to the attached drawings in which:

FIG. 1 is a schematic diagram of a related art format PPDU as defined bythe IEEE 802.11 protocol;

FIG. 2 is a diagram illustrating that a legacy station with a lowtransmission rate is incapable of performing virtual carrier sensingwhen a plurality of stations having a variety of transmissioncapabilities coexist;

FIG. 3 is a diagram illustrating a method of transmitting a responseframe according to an exemplary embodiment of the present invention;

FIGS. 4A and 4B are diagrams illustrating data structures of a PPDUtransmitted and received by an HT station;

FIG. 5 is a diagram showing a procedure in which a receiving unittransmits a legacy response frame when a transmitting unit transmits anHT data using channel bonding according to an exemplary embodiment ofthe present invention;

FIG. 6 is a diagram showing a procedure in which a receiving unittransmits a legacy response frame when a transmitting unit transmits anHT data using channel bonding according to another exemplary embodimentof the present invention;

FIG. 7 is a diagram showing a procedure in which a receiving unittransmits a legacy response frame when the transmitting unit transmitsan HT data without using channel bonding;

FIG. 8 is a schematic illustrating an HT station of transmitting legacyformat data according to an embodiment of the present invention; and

FIG. 9 is a flowchart illustrating a procedure in which an HT stationreceives an HT frame and transmits a legacy frame as a response frameaccording to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION

The present invention and methods of accomplishing the same may beunderstood more readily by reference to the following detaileddescription of exemplary embodiments and the accompanying drawings. Thepresent invention may, however, be embodied in many different forms andshould not be construed as being limited to exemplary embodiments setforth herein. Rather, these exemplary embodiments are provided so thatthis disclosure will be thorough and complete and will fully convey theconcept of the invention to those skilled in the art, and the presentinvention will only be defined by the appended claims. Like referencenumerals refer to like elements throughout the specification.

A method and apparatus for transmitting and receiving legacy format datain an HT wireless network is described hereinafter with reference toflowchart illustrations of methods according to exemplary embodiments ofthe invention. It will be understood that each block of the flowchartillustrations, and combinations of blocks in the flowchartillustrations, can be implemented by computer program instructions.These computer program instructions can be provided to a processor of ageneral purpose computer, special purpose computer, or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions, which are executed via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions specified in the flowchart block or blocks.

These computer program instructions may also be stored in a computerusable or computer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer usable orcomputer-readable memory produce an article of manufacture includinginstruction means that implement the function specified in the flowchartblock or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions that are executed on the computer or other programmableapparatus provide steps for implementing the functions specified in theflowchart block or blocks.

Each block of the flowchart illustrations may represent a module,segment, or portion of code, which comprises one or more executableinstructions for implementing the specified logical functions. It shouldalso be noted that in some alternative implementations, the functionsnoted in the blocks may occur out of the order. For example, two blocksshown in succession may in fact be executed substantially concurrentlyor the blocks may sometimes be executed in the reverse order, dependingupon the functionality involved.

HT wireless networks according to exemplary embodiments of the presentinvention include wireless networks capable of transmitting andreceiving HT data, e.g., an HT wireless network complying with the IEEE802.11n protocol, a wireless network having compatibility with one ofthe legacy format IEEE 802.11a, 802.11b, and 802.11g standards, and soon.

FIG. 3 is a diagram illustrating a method of transmitting a responseframe according to an exemplary embodiment of the present invention.

Referring to FIG. 3, a transmitter-side HT STA 101, a receiver-side HTSTA 102, an additional HT STA 103, and a legacy station 201 exist in awireless network. In operation S10, the transmitter-side HT STA 101transmits HT data to the receiver-side HT STA 102. As stated above, theHT data is transmitted at a high rate using a channel bonding or MIMOtechnique. The HT stations include stations enabling high rate datatransmission, e.g., stations in compliance with the IEEE 802.11nprotocol. Since the receiver-side HT STA 102 and the additional HT STA103 can interpret HT data, they perform virtual carrier sensing.However, since the legacy station 201 is not capable of interpreting HTdata, it cannot perform virtual carrier sensing. Instead, the legacystation determines that a medium is currently busy, thereby performingphysical carrier sensing. After completing of transmission of the HTdata, operation S11 begins and the legacy station 201 waits for theduration of an EIFS before it performs a backoff.

If the transmitter-side HT STA 101 completes transmission of the HTdata, the procedure goes to operation S11. At this time, thereceiver-side HT STA 102 transmits a legacy Ack after a duration of ashort inter-frame space (SIFS) to the transmitter-side HT STA 101. Thelegacy Ack is a response frame generated according to the IEEE 802.11a,802.11b, or 802.11g protocol. The legacy Ack can be transmitted to andreceived from both a legacy station and an HT station. After receivingeach legacy Ack, each of the HT stations 101, 102, and 103 capable ofinterpreting a legacy response frame goes to operation S12 after theduration of a DIFS, and then performs a backoff procedure.

In addition, since the legacy station 201 is capable of interpreting alegacy Ack frame but incapable of interpreting HT data, it is allowed towait for the duration of the DIFS in operation S12 to prohibit thelegacy station 201 from performing the backoff procedure. Consequently,the legacy station 201 is able to participate in the backoff procedureas well as the HT stations 101, 102, and 103, thereby avoidingperformance deterioration.

FIGS. 4A and 4B are diagrams illustrating a data structure of a PPDUtransmitted and received by an HT station.

The HT station enables data transmission and reception in two ways, bothof which start with legacy preambles, so that a legacy station caninterpret data transmitted/received by the HT station with legacypreamble.

As shown in FIG. 4A, a legacy format PPDU 30 includes a legacy preambleincluding a Legacy Short Training Field (L-STF), a Legacy Long TrainingField (L-LTF) and a Legacy Signal Field (L-SIG), and a Legacy Data(DATA) payload. Similar to FIG. 1, the L-SIG includes RATE, Reserved,LENGTH, and Parity fields. The legacy format PPDU 30 has the DATApayload following the L-STF, L-LTF, L-SIG fields containing informationregarding power management, signal and so on, respectively. Thus, thelegacy format PPDU 30 can be interpreted by both an HT station and alegacy station.

As shown in FIG. 4B, when a PPDU 40 has an HT preamble added to a legacypreamble, the HT station considers the PPDU 40 as being HT data. The HTpreamble contains information regarding HT data. The HT preambleconsists of an HT signal field (HT-SIG), an HT short training field(HT-STF), and an HT long training field (HT-LTF). In detail, the HT-SIGconsists of multiple fields including a LENGTH field defining a lengthof HT data, an MCS field defining modulation and coding schemes, anAdvanced coding field specifying the presence of advanced coding, aSounding packet field indicating whether transmission has been performedon all antennas, a number HT-LTF field specifying the number of HT-LTFsin a transmitted PPDU, a Short GI field specifying a short guardinterval in a data region of a frame, a ScramblerINIT field specifyingan initial value of a scrambler, 20/40 indicating whether the PPDU isconverted into a signal at a bandwidth of 20 or 40 MHz, a CRC field forerror checking, and a Tail field. As shown in FIG. 4B, HT-SIG, HT-STF,HT-SIG, . . . , HT-LTF, each contain a specific number of bits, followedby HT data.

As shown in FIG. 4B, if short data is transmitted in the HT PPDU 40, aconsiderable increase in the HT preamble is caused, therebysignificantly increasing overhead. Thus, in order to transmit framesincluding only short data, e.g., Ack or control frames, it is efficientto use the legacy PPDU 30. In addition, the legacy PPDU 30 enables alegacy station to perform virtual carrier sensing when the legacystation exists in a wireless network.

FIG. 5 is a diagram showing a procedure in which a receiving unittransmits a legacy response frame when a transmitting unit transmits anHT data using channel bonding according to an exemplary embodiment ofthe present invention.

When a transmitting unit selects two adjacent channels of a currentchannel, that is, the current channel and a directly next channel or adirectly previous channel and the current channel, bonded to each other,and transmits the same to a receiving unit, the receiving unit receivesthe same and transmits a legacy Ack to each channel. FIG. 5 shows anexample in which each antenna is incapable of handling differentchannels. A receiver-side HT STA employs an overlap mode in which datacontaining a legacy response frame 30 overlaps from a lower sub-channelto an upper sub-channel through a single antenna 181. In such aninstance, the legacy response frame 30 can be transmitted through theupper and lower sub-channels. In addition, the legacy response frame 30can be received by HT stations and legacy stations existing in the upperand lower sub-channels. A PPDU including a legacy response frameconsists of an L-STF (Legacy Short Training Field), an L-LTF (LegacyLong Training Field), an L-SIG (Legacy Signal Field), and a DATA (LegacyData) payload, as described above with reference to FIG. 4.

FIG. 6 is a diagram showing a procedure in which a receiving unittransmits a legacy response frame when a transmitting unit transmits anHT data using channel bonding according to another exemplary embodimentof the present invention, in which antennas 181 and 182 transmit data todifferent channels, unlike in FIG. 5.

When the transmitting unit selects two adjacent channels of a currentchannel, that is, the current channel and a directly next channel or adirectly previous channel and the current channel, bonded to each other,and transmits the same to the receiving unit, the receiving unitreceives the same and transmits a legacy Ack to either channel. Unlikein FIG. 5, the respective antennas 181 and 182 are capable of handlingdifferent channels. The receiving unit accesses lower and uppersub-channels using the respective antennas 181 and 182 and transmits thesame legacy Ack frame 300. A structure of a legacy format frame is thesame as described in FIG. 4.

Legacy format data is simultaneously transmitted to both a controlchannel and an extension channel in response to a frame transmittedusing channel bonding, as shown in FIG. 5 and 6, which allows the legacyformat data to be received by stations in the extension channel as well.

FIG. 7 is a diagram showing a procedure in which a receiver-side HTstation transmits a legacy response frame when the transmitter-side HTstation transmits HT data using an MIMO technique according to anexemplary embodiment of the present invention.

When the transmitter-side HT station transmits HT data using an MIMOtechnique, the receiver-side HT station utilizes one antenna 181 totransmit a legacy response frame via a current channel. Thetransmitter-side HT station is capable of receiving the legacy responseframe received through the current channel. Other HT stations caninterpret the legacy response frame to enable virtual carrier sensing.Further, legacy stations communicating via the current channel can alsointerpret the legacy response frame to enable virtual carrier sensing. Astructure of a legacy format frame is the same as described in FIG. 4A.

As illustrated in FIGS. 5 through 7, the receiver-side HT STA 102transmits the legacy PPDU 30 in various manners according to thetransmission method employed by the transmitter-side HT STA 101. Thereceiver-side HT STA 102 can be informed of the transmission methodemployed by the transmitter-side HT STA 101 from MCS values in theHT-SIG field of the HT PPDU shown in FIG. 4B. That is, the number ofantennas used in data transmission or the number of spatial streams,modulation schemes used, coding rate, guard interval, and use or non-useof channel bonding (40 MHz) can be deduced from the MCS valuesenumerated in the Table below. Table 1 illustrates an exemplarymodulation and coding scheme (MCS) table. TABLE 1 Number Modulation GI =800 ns GI = 400 ns MCS of streams schemes Coding rate 20 MHz 40 MHz 20MHz 40 MHz 0 1 BPSK 1/2 6.50 13.50 7.22 15.00 1 1 QPSK 1/2 13.00 27.0014.44 30.00 2 1 QPSK 3/4 19.50 40.50 21.67 45.00 3 1 16-QAM 1/2 26.0054.00 28.89 60.00 4 1 16-QAM 3/4 39.00 81.00 43.33 90.00 5 1 64-QAM 2/352.00 108.00 57.78 120.00 6 1 64-QAM 3/4 58.50 121.50 65.00 135.00 7 164-QAM 5/6 65.00 135.00 72.22 150.00 8 2 BPSK 1/2 13.00 27.00 14.4430.00 9 2 QPSK 1/2 26.00 54.00 28.89 60.00 10 2 QPSK 3/4 39.00 81.0043.33 90.00 11 2 16-QAM 1/2 52.00 108.00 57.78 120.00 12 2 16-QAM 3/478.00 162.00 86.67 180.00 13 2 64-QAM 2/3 104.52 216.00 116.13 240.00 142 64-QAM 3/4 117.00 243.00 130.00 270.00 15 2 64-QAM 5/6 130.00 270.00144.44 300.00 16 3 BPSK 1/2 19.50 40.50 21.67 45.00

An HT station can transmit not only the Ack frame but also an PPDU of acontrol frame including short data such as a CTS frame or an RTS frame.During legacy format transmission, it is not necessary add an HTpreamble to the data, a legacy station can perform virtual carriersensing, thereby reducing overhead.

In a case of a considerable amount of data, an HT format PPDU istransmitted. In a case of short data, that is, a small amount of data,e.g., a control frame, a legacy format PPDU is transmitted, therebyreducing a total amount of data transmitted and received in the overallwireless network and implementing a wireless network in which the HTstation and a legacy station coexist.

The term “unit” as used herein, means, but is not limited to, a softwareor hardware component or module, such as a Field Programmable Gate Array(FPGA) or Application Specific Integrated Circuit (ASIC), which performscertain tasks. A unit may advantageously be configured to reside on theaddressable storage medium and configured to be executed on one or moreprocessors. Thus, a unit may include, by way of example, components,such as software components, object-oriented software components, classcomponents and task components, processes, functions, attributes,procedures, subroutines, segments of program code, drivers, firmware,microcode, circuitry, data, databases, data structures, tables, arrays,and variables. The functionality provided for in the components andunits may be combined into fewer components and modules or furtherseparated into additional components and units. In addition, thecomponents and units may be implemented such that they are executed onone or more CPUs in a communication system.

FIG. 8 is a schematic illustrating an HT station which transmits legacyformat data according to an exemplary embodiment of the presentinvention. The HT station 100 includes a transmitting unit 110, areceiving unit 120, an encoding unit 130, a decoding unit 140, acontrolling unit 150, a legacy transmission controlling unit 160, andtwo antennas 181 and 182. The antennas 181 and 182 receive and transmitwireless signals.

The transmitting unit 110 transmits signals to the antennas 181 and 182,and the encoding unit 130 encodes data to generate signals to betransmitted to the antennas 181 and 182 by the transmitting unit 110. Inorder to transmit signals via two or more antennas using an MIMOtechnique, the signal data must be divided and then encoded separately.Alternatively, in order to transmit signals using channel bonding, thetransmitting unit 110 selects two adjacent channels, including a currentchannel and a directly next channel or a directly previous channel, tobe bonded to each other, and transmits the signals via the bondedchannels.

The receiving unit 120 receives signals from the antennas 181 and 182,and the decoding unit 140 decodes the signals received by the receivingunit 120 into data. When the data is received using an MIMO technique,it is necessary to integrate the data transmitted via the two channels.

The legacy transmission controlling unit 160 controls short-length data,e.g., an Ack frame, a CTS frame, or an RTS frame, to be transmitted in alegacy format. The control unit 150 manages and controls the exchange ofinformation among various elements of the HT station 100.

FIG. 9 is a flowchart illustrating a procedure in which an HT stationreceives an HT frame and transmits a legacy frame as a response frameaccording to an exemplary embodiment of the present invention.

The HT station accesses a wireless network in operation S301. In thiscase, the accessing the wireless network encompasses not only accessingan existing wireless network but also newly generating a wirelessnetwork. In an exemplary embodiment, operation S301 may includegenerating a basic service set (BSS), e.g., an Access Point (AP). Next,a first station existing in the wireless station receives first datacompliant with a first protocol in operation S302. The first protocolincludes protocols transmitted and received in an HT format, e.g., theIEEE 802.11n protocols. In addition, the first protocol may includeprotocols having downward compatibility with legacy format protocols.

The term “downward compatibility” used herein means that an upgradedprotocol or software is compatible with past proposed protocols orsoftware. For example, the IEEE 802.11n protocols can interpret datathat is transmitted and received in the IEEE 802.11a, 802.11b, or802.11g protocol, and can transmit/receive HT data in the IEEE 802.11a,802.11b, or 802.11 g protocol. The same is true when upgraded softwareis available to allow data generated from existing version software tobe interpreted or managed.

After receiving the first data, it is determined whether the first datais transmitted using channel bonding in operation S310. If the firstdata is transmitted using channel bonding (YES in operation S310),second data compliant with a second protocol is transmitted via therespective channels used with channel bonding in operation S320.According to the second protocol, frames that can be interpreted bylegacy stations receiving channels associated with channel bonding aretransmitted. Thus, if the first protocol is compliant with the IEEE802.11n, the second protocol includes protocols with which the IEEE802.11n protocol is downward compatible, e.g., IEEE 802.11a, 802.11b,802.11g, or the like. The transmission procedures have been describedabove with reference to FIG. 5.

If the first data is transmitted without using channel bonding (NO inoperation S310), that is, if the first data is transmitted using, e.g.,an MIMO technique, second data compliant with the second protocol istransmitted in operation S330. The transmission procedure has beendescribed above with reference to FIG. 6. As described above, the secondprotocol includes protocols with which the first protocol is downwardcompatible.

The wireless network shown in FIG. 8 may be an BSS with an AP, or anIndependent Basic Service Set (IBSS) without an AP. The second data isshort data including control frames, such as Ack, CTS, RTS, etc.

The second data can be interpreted by legacy stations, so that thelegacy stations can perform virtual carrier sensing. Accordingly, theuse of the second data enhances transmission efficiency in a wirelessnetwork without legacy stations.

As described above, according to exemplary embodiments of the presentinvention, when HT stations and legacy stations each having differenttransmission capabilities coexist in a wireless network, the legacystations can perform virtual carrier sensing.

In addition, according to exemplary embodiments of the presentinvention, short data is transmitted in a legacy format, therebyenhancing transmission efficiency.

It will be understood by those of ordinary skill in the art that variouschanges in form and details may be made therein without departing fromthe spirit and scope of the present invention as defined by thefollowing claims. Therefore, it is to be appreciated that the abovedescribed exemplary embodiments are for purposes of illustration onlyand not to be construed as a limitation of the invention. The scope ofthe invention is given by the appended claims, rather than the precedingdescription, and all variations and equivalents which fall within therange of the claims are intended to be embraced therein.

1-30. (canceled)
 31. A method of transmitting data at a station in awireless network, the method comprising: receiving a data frame via abonded channel which is formed by channel bonding first and secondadjacent channels; and separately transmitting an acknowledgement (Ack)frame via each of the first and the second adjacent channels withoutchannel bonding in response to the data frame.
 32. The method of claim31, wherein the wireless network is compliant with the IEEE 802.11nstandard, the first data is compliant with the IEEE 802.11n standard,and the Ack frame is compliant with the IEEE 802.11a standard, the IEEE802.11b standard, or the IEEE 802.11g.
 33. The method of claim 31,wherein the transmitting the Ack frame comprises: transmitting the Ackframe via the first adjacent channel by a first antenna; andtransmitting the Ack frame via the second adjacent channel by a secondantenna.
 34. The method of claim 31, wherein the data frame is compliantwith a first protocol and the Ack frame is compliant with a secondprotocol, and the first protocol is downward compatible with the secondprotocol.
 35. A wireless network apparatus comprising: a receiving unitwhich receives a data frame transmitted via a bonded channel which isformed by channel bonding first and second adjacent channels; and atransmitting unit which separately transmits an acknowledgement (Ack)frame via each of the first and the second adjacent channels withoutchannel bonding, in response to the data frame.
 36. The wireless networkapparatus of claim 35, wherein the wireless network is compliant withthe IEEE 802.11n standard, the first data is compliant with the IEEE802.11n standard, and the ACK frame is data compliant with the IEEE802.11a standard, the IEEE 802.11b standard, or the IEEE 802.11gstandard.
 37. The wireless network apparatus of claim 35, wherein thetransmitting unit transmits the Ack frame separately and simultaneouslyto each of the first and the second adjacent channels.
 38. The wirelessnetwork apparatus of claim 37 further comprising first and secondantennas, wherein the transmitting unit transmits the Ack frame via thefirst adjacent channel using the first antenna and transmits the Ackframe via the second adjacent channel using the second antenna.
 39. Thewireless network apparatus of claim 35, wherein the data frame iscompliant with a first protocol and the Ack frame is compliant with asecond protocol and wherein the first protocol is downward compatiblewith the second protocol.
 40. The method of claim 31, wherein the bondedchannel is a 40 MHz channel and each of the first and second channels isa 20 MHz channel.
 41. The wireless network apparatus of claim 35,wherein the bonded channel is a 40 MHz channel and each of the first andsecond channels is a 20 MHz channel.